This proposal requests support for new equipment to upgrade the sole facility for flow cytometry and cell sorting available for research investigation in the Medical School of the University of Minnesota. The existing facility has a single Becton-Dickinson FACS IV, purchased in 1980. There are two major justifications for the proposed upgrade: 1) The existing facility is heavily used and cannot meet current demands even for routine analysis and sorting; 2) Although the FACS IV has been upgraded to allow dual wavelength excitation and four parameter analysis, the users all have research that requires or would be greatly enhanced by state-of-the-art methods requiring 5 or more detectors for analysis. Examples include 3- and 4-color immunofluorescent analysis and sorting of complex cell mixtures and combinations of immunofluorescent analysis with fluoroprobes for intracellular calcium, PH or cell cycle analysis. To meet these needs currently the major users have had to rely on outside collaboration and limited access to instruments at other institutions. The request is supported by the major users of the facility all with current NIH Projects involving flow cytometry. The principal focus of currently funded research supported by these grants is on lymphocyte differentiation and function: functional maturation of T and NK cells; analysis of normal and leukemic B cell precursors; signal transduction in normal T cells; analysis and radiosensitivity of normal and leukemic progenitor cells; and evaluation of immunotoxins in human bone marrow transplantation. The proposed FACStar Plus system will meet the acute need for state-of-the-art flow cytometry and sorting. The proposed FACScan system has one more detector for analysis than the existing instrument, will provide an accessible, user-friendly instrument to meet increasing demands for immunofluorescent analysis, and will free the major instrument for cell sorting and advanced applications.